.btn{
   color: red;
   font-size: 30px;
}
.red{
   color:red
}
.big{
   font-weight: bold;
}
.box{
   border:1px solid red;
   text-align: center;
   line-height: 100px;
   width:100px;
   height:100px;
}

/*公共样式*/
*{
   margin:0;
   padding:0;
}